Switch



l-ALHIIHIU March 12, 1940. A. RAMSEY ,193,238

SWITCH Filed Dec. 14, 1936 4 Sheets-Sheet 1 Q) Q txammer NAKERS fig BREAKERS,

March 12, 1940. A. RAMSEY SWITCH 4 Sheets-Sheet 2 Filed Dec. 14, 1936 EXEIiTHi'K-BF 4UU. QLUJHHJHY- CIRCUIT March 12, 1940. RAMSEY 2,193,238

SWITCH Filed Dec. 14, 1936 4 Sheets-Sheet 3 Lxammer MAKERS a BREAKERS, 1 6 2 March 12, 1940.

A. RAMSEY 2,193,238

SWITCH Filed Dec. 14, 19:6 4.Sheets-Sheet 4 l'ibUil UNITED STATES PATENT OFFICE SWITCH Allan Ramsey,

Evanston,

Ill., assignor to Schweitzer & Conrad, Inc., Chicago, 111., a corporation of Delaware My invention relates generally to switches for opening and closing an electric circuit, and it has particular relation to disconnecting switches and contact assemblies that are not intended to be opened under load.

In electric switches of the disconnecting type that have been in use for many years, reliance is placed upon surface contact engagement between the relatively moving switch members in order to provide a circuit therethrough. Such switches comprise one or more blades formed usually of plate copper bar material that are arranged to engage an appropriate number of switch jaws of like material. The movable switch member rotates in a similar jaw and is intended to have surface contact engagement therewith. While it is possible to obtain substantially surface contact engagement between the relatively movable switch members by careful machining and aligning thereof in the original installation, this condition is not maintained, and, after the switch has been in operation for some time, line or point contact engagement is actually present between the relatively movable switch members rather than surface contact engagement. As a result, the effective capacity of the switch for carrying current is considerably reduced because of the undue heating effects that are produced under these conditions if rated current is caused to flow through the switch.

In a given switch having a given current carrying capacity there is a definite relationship between the area of contact engagement and the contact pressure. Thus, if a large contact area is actually present, then a smaller contact pressure is required for the same current capacity and vice versa. In the conventional knife blade switch the contact area usually becomes, after use, a point or line contact surface and, since the contact pressure is not ordinarily increased, the current conducting capacity of the switch with permissible temperature rise is reduced. It has been proposed to construct a switch employing a single point contact engagement with a contact surface. In such case a tremendous contact pressure is required to obtain the necessary relationship between contact area and contact pressure. This type of switch requires relatively massive construction of the relatively movable switch members and they are substantially inflexible. It also requires accurate aligning or machining of the clamping mechanisms. It will be apparent that small area high pressure contact engagement provides a satisfactory solution to the problem of switch contact engagement but it will also be apparent that more than single point contact engagement should be provided in order to provide a switch that can be easily operated with a simple cperatmg mechanism and having contact members that will last indefinitely.

Instead of attempting to obtain surface contact engagement between the relatively movable switch members, which is impossible from a practical operating standpoint, or to utilize single point contact engagement, I have provided a switch construction that relies solely upon a plurality of small area high pressure contact engagements, between the relatively movable switch members. In my copending application, Serial No. 445,548, filed April 19, 1930, Patent No. 2,063,954, and assigned to the assignee of this application, I have disclosed an embodiment of this type of switch in which the stationary switch members comprise contact assemblies formed by flexible spring wire fingers having double convex surfac'es'for substantially point contact engagement with the contact surfaces of a pair of spaced apart switch blades that are arranged to operate as a single unit. In another embodiment of the switch disclosed in this copending application, the contact fingers are mounted on the switch blade and are arranged to individually engage the stationary contact members. It is not only desirable to provide point contact engagement between the spring wire fingers and the switch blades, but it is also desirable to provide a relatively high contact pressure therebetween. Moreover, the contact pressure applied to each finger should be about the same and should remain constant throughout the life of the switch. In my copending application, reliance is placed upon the inherent resilieg g of the spring wire contact fingers typ'Fd vid'e the necessary contact pressure. Stop members are provided for limiting the relative movement of the spring wire contact fingers to position them slightly within the path of relative mc.ement with the corresponding contact surfaces of the switch blades. In this manner the contact fingers are prestressed and the full resilient effect thereof is available to provide the relatively high contact pressure as soon as contact engagement takes place and the contact fingers are moved from engagement with the stop means.

The provision of a plurality of individually movable and resilient contact fingers having small area contact engaging portions takes care of any slight misalignment that may be present between the fingers. Each contact finger conducts its share of the total current, and there is no tendency for the current flow to concentrate in one or a few of the total number of contact fingers. At the same time, because of the use of a plurality of contact fingers, the pressure that is required to be applied to each finger is relatively small as compared to a single point contact engagement and yet the necessary relationship between contact area and contact pressure is provided. Furthermore, relatively little effort is required to operate the switch from and to the switch closed position.

In the construction disclosed in my copending application, the current flows through the spring contact fingers, and thus tends to raise the tempcrature thereof. As a result of this heating under severe over current conditions, the contact fingers may lose their resilient characteristics, and the desired contact pressure may not be provided as desired. The effectiveness of the point contact engagement may then be correspondingly reduced.

It has been the practice in the prior art to provide direct contact engagement between switch members formed of copper. It is well known that the contact surfaces become'corroded, particularly when the switch remains in one position for a considerable period. When the switch is closed under these conditions, a relatively high resistance contact surface engagement is present which may cause undue heating of the switch. It has been proposed to plate the contact surfaces of the relatively movable switch members with a coating, of sil-.

ver, the contact surface characteristics of which are the most desirable of all materials that are known at the present time and which are practical from an operating and cost standpoint. The silver plated contact surfaces, usually formed by an electro-deposition process, are, in fact, not surfaces, but instead comprise a plurality of minute particles of silver that have been deposited on the switch member which is usually copper. This construction does not furnish the desired corrosion resisting characteristics for the contact surfaces since a porous rather than a solid silver coating is present. The use of solid silver or solid silver alloy avoids these difficulties but it is expensive. If the switch members of a conventional knife switch are provided with solid silver surfaces, the cost becomes prohibitive. Furthermore, it will be obvious that the silver in such a switch is not used efficiently after it has been in use for some time, since point or line contact engagement is present rather than surface contact engagement. It is impractical to employ silver in the switch in which only single point contact engagement is employed because it is not capable of resisting the relative movements necessary under the very high pressures that are involved.

It is, therefore, an important object of the present invention to employ the principles of switch construction set forth in my said copending application and to modify them in the construction and arrangement of switches having improved operating characteristics.

Another important object of my invention is to provide a resilient effect independent of that inherent in the prestressed spring wire contact fingers for the purpose of obtaining a predetermined uniform contact pressure throughout the life of the switch.

Still another important object of my invention is to provide silver contact engagingportions of limited area in the relatively movable members of a switch of the type in which substantially point contact engagement in contradistinction to surface contact engagement takes place.

A further important object of my invention is to position a relatively narrow silver strip on one contact member of a switch for point contact engagement with silver inserts positioned in individually movable contact fingers, thereby providing contact engaging portions therebetween having substantially uniform characteristics throughout the life of the switch.

An object of my invention is to individually guide the spring wire contact fingers to prevent distortion thereof during operation of the switch, and at the same time to limit the movement thereof in such manner as to produce a prestressing effect.

Another object of my invention is to provide a maximum number of point contact engagements between a pair of relatively movable generally cylindrical switch members within a limited space.

A further object of my invention is to individually and resiliently back up each spring wire contact finger of a row of contact fingers to obtain a relatively high contact pressure.

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

My invention, accordingly, is disclosed in the embodiments hereof shown in the accompanying drawings, and it comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following detailed description taken in connection with the accompanying drawings, in which:

Figure l is a view, partly in side elevation and partly in section, illustrating one concrete embodiment of my invention;

Figure 2 is a fragmentary view, partly in side elevation and partly in section, showing at an enlarged scale the manner in which the silver inserts and the silver strip are positioned;

Figure 3 is a view, partly in side elevation and partly in section, showing other details of construction of one of the contact members of Figure 1;

Figure 4 is a sectional view taken along the line 4-4 of Figure 1;

Figure 5 is a sectional view taken along the line 5-5 of Figure 1;

Figure 6 is a fragmentary end view of one of the contact members shown in Figure 1;

Figure '7 is a view, in side elevation, of a disconnecting switch that employs certain of the features of construction of the switch shown in Figure 1;

Figure 8 is a view, in front elevation, of the switch shown in Figure 7;

Figure 9 is a view, in side elevation, and at an enlarged scale, of the switch blade and stationary contact members of the switch shown in Figure 7;

Figure 10 is a sectional view taken along the line l0l0 of Figure 9;

Figure 11 is a view similar to Figure 10 and showing the positions of the flexible contact fingers just prior to contact engagement therewith by the switch blades;

MAKERS a BRLAKERS,

Figure 12 is a view, in side elevation, of one of the blades of the switch shown in Figure 9;

Figure 13 is a sectional view taken along the line l3-l3 of Figure 12;

Figure 14 is a view, in side elevation, of one of the contact fingers; and

Figure 15 is a view, in front elevation, of one of the contact fingers in conjunction with a fragmentary portion of one of the switch blades, certain parts being broken away in order to more clearly illustrate the invention.

According to one embodiment of my present invention, I have provided a plug and socket assembly for conducting relatively high values of current that is particularly adapted for use in connection with the truck type circuit breaker that is adapted to be inserted in or withdrawn from a circuit as a unit. In such a construction, relatively little space is available and, therefore, a compact arrangement of the engaging contact members must be provided. In addition it is desirable to provide a contact arrangement that may be easily operated. For this purpose I have provided a socket having two concentric rows of spring wite contact fingers and a plug having a pair of concentric cylindrical contact surfaces for individually engaging the rows of contact fingers. The outer ends of the contact fingers are curved to provide substantially point contact engagement with the corresponding contact surface of the plug. The inherent resiliency of the spring wire contact fingers is augmented by a coil spring that surrounds each of the concentric rows of contact fingers in the plane of contact engagement with the plug where efficient use of its resiliency may be had. A cylindrical stop member is provided individual to. each row of contact fingers, and it is secured to the base of the socket at one end and at its other end it is provided with a flange that is disposed substantially in the plane containing the free outer ends of the contact fingers. The flange is provided with radial slots, each individual to one of the fingers to. limit the movement thereof under the combined influence of the springs and the inherent resiliency of the contact fingers. In addition the slots prevent radial and circumferential distortion of the contact fingers when the plug is moved into and out of contact engagement therewith. At the curved portion of each of the contact fingers, a silver insert is provided and a corresponding narrow band of silver is provided on the contact surface of the plug individual thereto. Since only point contact engagement in a plane is required, the quantity of silver that is used is reduced to a minimum, and thus a relatively inexpensive construction is provided. While it is preferable to employ silver inserts, it will be understood that they may be omitted or other metals used in lieu thereof without departing from the scope of the present invention.

In another embodiment of the invention, a pair of rotatably mounted switch blades is arranged to engage a double row of hairpin or U-shaped contact fingers on each of a pair of stationary switch contact members. A portion adjacent the outer end of each of the contact fingers is bowed outwardly to provide the point contact engagement with the corresponding contact surface of the switch blades. A silver insert is provided in each of the bowed portions of the contact fingers, and a narrow strip of silver is provided in the corresponding contact surface of the switch blades in order to provide the contact engaging portions therebetween.

LKdHHnGr Referring now particularly to Figure 1 of the drawings, it will be observed that the reference character 20 designates, generally, a socket contact member and the reference character 2| designates, generally, a plug contact member. Either the socket 20 of the plug 2| may be considered as a movable contact or switch member, while the other may be considered the stationary contact or switch member. Thus, for example, the socket 20 may be mounted on the circuit breaker, and the plug 2| may be stationarily mounted in the switch structure, in which case the socket 20 may be termed the movable contact or switch member. However, it will be understood that their function may be reversed as appears to be desirable.

The plug 2| comprises a terminal member 22 that may be in the form of a copper rod having the necessary cross sectional area to provide the required current carrying capacity and mechanical strength. In order to permit maximum contact engagement with the terminal member 22, it is provided at one end with concentric contact members 23 and 24. It will be observed that the contact member 23 comprises a hollow cylinder integrally formed with the terminal member 22, and that the contact member 24 comprises a solid cylindrical contact member. In this manner provision is made not only for contact engagement with the outer periphery of a portion of the terminal member 22, but also provision is made for making contact engagement with a central portion thereof as well.

As indicated hereinbefore, it is desirable to provide a silver contact engaging surface rather than to depend solely upon the conductivity of the contact surface of the copper terminal member 22. For this purpose a narrow band of solid silver or solid silver alloy 25 is soldered to and rolled into or otherwise intimately associated with mapper ring 2'! that is sweat soldered to the outer surface of the cylindrical contact member 23. This construction is illustrated more clearly in the enlarged view thereof shown in Figure 2 of the drawings. In like manner, the solid cylindrical contact member 24 is provided with a narrow band of silver 28 that is rolled into a copper ring 30 which is secured theretdb'y soldering. It will then be apparent that each of the contact members 23 and 24 is provided with a narrow band or strip of silver that is integrally bonded thereto and which comprises the contact surface thereof. The manner in which this bond is provided will be set forth in detail hereinafter. Since the contact surface characteristics of silver are all that are required and, as will appear hereinafter, since only point contact engagement, which can be provided in a line or plane, is required therewith, it will be obvious that a minimum weight of silver is required having little width and thickness and it is used very efficiently.

The terminal member 22 is provided with a pair of laterally extending bars 3| to provide for electrical connection thereto as will be readily understood. A sleeve 32 of insulation is provided around the terminal member 22 in order to suitably insulate it from the supporting structure in which it may be mounted and to prevent a person from coming in contact engagement therewith.

The socket 20 comprises a solid cylindrical base member 35 having a rearwardly extending boss 36 which is provided with suitable slots for receiving conductor bars 3'! to permit connection thereto. The base member 35 carries a sleeve 38 of insulation that may be mounted thereon by a locking ring 39. It will be observed that the looking ring 39 is positioned in suitable registering grooves in the base member 35 and the sleeve 38, and, as shown more clearly in Figure 4 of the drawings, it is of zig-zag shape and is formed of resilient material to permit assembly and retention in operative position. The base member 35 is substantially sealed to the sleeve 38 by a packing ring 40, formed preferably of asbestos or like material, that may be positioned in a suitable groove in a clamp ring 4| that is secured by screws 42 to the base member 35, as illustrated. On the front side of the base member 35 a stop pin 43 is positioned in alignment with the contact member 24 for the purpose of accurately positioning the plug 2| in the socket 20. Obviously the contact member 24 may be extended to engage the front surface of the base member 35, in which case the stop pin 43 could be omitted.

With a view to providing substantially point contact engagement with the narrow bands of silver 25 and 28 on the terminal member 22, two rows of spring wirg p orrtact fingers 44 and 45 are providedfTh s'pring wire's4'4 and 45, or eacffof the spring wire fingers forming the rows 44 and 45, are positioned in closely fitting drilled holes in the front surface of the base member 35 and are rigidly secured therein by peeping, at the points 4 5 a n d 41 adjacent these holes, as indicated more clearly in Figure 5 of the drawings. In this manner, the contact fingers are rigidly supported at one end as cantilevers.

The point contact engagement is provided by the inwardly curved outer end portions 48 and 49 of the contact fingers that are preferably formed of wire, thereby providing a double convex contact surface. At each of these inwardly curved portions 48 and 49, silver inserts 50 and 5| are positioned in the form of solid silver or silver alloy rivets. As indicated more clearly in Figure 2 of the drawings, the silver insert 50 is so shaped as to conform to the convex portion 48 of the contact finger 44. In this manner, substantially point contact engagement is provided between the narrow silver strip 25, for example, on the plug 2| and the silver insert or rivet 50 on the contact finger 44 of the socket 20. Since the contact surface of the insert 50 is of double convex shape, a plane or oppositely curved surface has only point contact engagement therewith as is desired.

Because of the use of a plurality of small area high pressure contact surfaces as provided by the individually flexible contact fingers, it becomes practical to employ solid silver to form the contact engaging surfaces. Each of the silver inserts 50 and 5| is relatively small, and consequently the cost is comparatively slight. Since the inserts 50 and 5| are positioned substantially in a single plane and always engage the contact members 23 and 24 at the same places in substantially a plane, the bands of silver 25 and 2 need only be of slight width. In this manner the advantages of silver contact surfaces are obtained with a minimum of expense.

While I have disclosed the use of solid silver or silver alloy to form the contact engaging portions in either or both of the switch members, since that material at the present time appears to be the most satisfactory, it will be understood that any material having similar characteristics or properties, which may later be discovered, may be employed in lieu of silver without departing from the scope of my invention. Furthermore, the insertsin oneof the switch membersinaybe ofiig jerent; materlaf'th'aii'- the inserts in theother smell member.

Although the spring wire contact fingers 44 and 45 are themselves inherently resilient and provide a considerable contact pressure between the silver engaging contact surfaces, it is desirable, for the reasons set forth hereinbefore, to provide an additional resilient force to maintain high contact pressure throughout the life of the device. It is for this purpose that coil tension springs 52 and 53 are positioned, respectively, about the rows 44 and 45 of contact fingers. It will be noted that the springs 52 and 53 are positioned in the curved portions of the contact fingers so that their reaction takes place substantially in the same plane as does the contact engagement. Thus the full resilient force of the springs 52 and 53 is utilized with a minimum of distortion thereof.

If some means were not provided for limiting the inward movement of the contact fingers 44 and 45, considerable difficulty would be encountered in moving them to the positions as shown in Figure 1 of the drawings, when the plug 2| is inserted into the socket 20. That is, it would be necessary to move the spring wire contact fingers 44 and 45 from this unstressed condition to the fully stressed positions shown in the drawings. Such action is rendered unnecessary by utilizing the principle of prestressing the contact fingers 44 and 45 as is set forth in my copending application, hereinbefore referred to. For the purpose of prestressing the contact fingers 44 and 45, cylindrical stop members 54 and 55 are provided. The stop members 54 and 55 are formed preferably of thin sheet material such as brass, and they are arranged to surround the rows of contact fingers 44 and 45 as illustrated. The stop member 54 is secured in a suitable recess in the base member 35 as by screws 56. The stop member 55 may be secured by screws 51 to a suitable outwardly extending fiange 58 in the front face of the base member 35. At the other ends of the stop members 54 and 55, inturned flanges 60 and BI are provided in which are positioned radially disposed slots 62 and 63, respectively. It will be observed that each of the slots 62 and 63 is individual to one of the spring wire contact fingers 44 and 45 and that the outer ends thereof projlect slightly therethrough. When the plug 2| is withdrawn from the socket 20, the outer ends of the contact fingers 44 and 45 about the inner ends of the slots 62 and 63, in which position the contact surfaces formed by the silver inserts 50 and 5| are positioned slightly within the path of relative movement with the silver bands or strips 25 and 28, respectively, to insure that each finger is lifted off of its stop. This position of the contact fingers 44 and 45 is illustrated more clearly in Figure 6 of the drawings. It will now be apparent that the movement of the socket 20 and plug 2| into contact engagement requires only a slight movement of the contact fingers 44 and 45 to lift them from engagement with the inner ends of their respective slots 62 and 63. This slight movement is caused by the beveled edges of the concentric contact members 23 and 24. The extent of the bevelling that is required is reduced to a minimum because the contact fingers 44 and 45 are prestressed by the stop members 54 and 55. As soon as they are thus lifted, the full resilient effects of the springs 52 and 53 and of the contact fingers 44 and 45 themselves are available to provide contact pressure between the silver contact surfaces. It will be obvious that this construction does not require a highly accurate alignment or adjustment of the contact fingers 44 and 45.

It will now be apparent that the double row of contact fingers 44 and 45 provides a maximum number of point contact engagements with theplug ZI and, at the same time, that a minimum ofspace is required therefor. Because of the pre-stressing action provided by the stop members 54 and 55 a minimum amount of work is required to effect contact engagement and disengagement. The coil springs 52 and 53 afford the necessary contact pressure, and the resiliency thereof is not affected to any appreciable extent by current fiow, because they are positioned out of the path of the main current fiow. If desired, they may be constructed of a stainless steel alloy, such as an alloy of iron, chromium and nickel known as 18-8, in order to retain their resiliency even when subjected to relatively high temperatures. The desired contact surface conditions are present because of the provision of the silver contact engaging portions in the plug 2| and the socket 20. At the same time. by the use of relatively small amounts of silver it is possible to reduce the cost of the device to a minimum. Since the free outer ends of the contact fingers 44 and 45 are confined in the radial slots 62 and 53, distortion thereof is prevented on movement into and out of contact engagement with the corresponding contact surfaces of the plug 2I.

Another embodiment of my invention is illustrated in Figures 7 through 15 of the drawings, and particular reference may now be had to Figures 7 and 8. As there shown, a disconnecting switch, illustrated generally at 58, is provided for mounting on a suitable channel-shaped support member 61 on which are mounted pin type insulators 68 and 69. Suitable adapters I and H are secured as by bolts I2 and I3 to the insulators 68 and 69, and they have respectively secured thereto terminal members I4 and I of plate-like construction and provided with suit.- able transverse apertures to permit connection thereto. Stationary switch contact members, shown generally at I6 and 11, are positioned respectively on the terminal members I4 and I5 and constitute circuit terminal members that are bridged by a switch blade shown generally at I8 and comprising a pair of switch blades I9 and 80 that are rotatably mounted by means of a transversely extending bolt 8| on the contact member I1. The switch blade 18 is moved into and out of engagement with the contact member I6, and locked and unlocked by-means of an operating mechanism, shown generally at 82. the details of construction of which will be set forth hereinafter. The operating mechanism 82 is mounted principally upon a bolt 83 which extends transversely through the blades I9 and 80. These blades are held in suitable spaced relationship by rivets 84 and 85, as illustrated. It will be understood that any other suitable form of mounting for the stationary contact members I6 and I1 may be provided. The mounting therefor that is illustrated in the drawings is merely typical of any suitable arrangement.

Referring now particularly to Figure 9 of the drawings, it will be observed that the stationary switch members 16 and 11 are provided, respectlvely, with base members 88 and 89 that are preferably formed of copper plate. Each of the base members 88 and 89 is provided, respectively, with four rectangular apertures 90 and SI for positioning therein sets of hairpin or U-shaped l-AUIHIIIUI spring wire contact fingers 92 and 93. In the particular embodiment of the invention disclosed,

. six contact fingers are positioned in each of the rectangular apertures 90 and 9|. It will be understood that a greater or a lesser number may be employed as desired. For assembly purposes and to provide the required spacing, the upper and lower sets of contact fingers 92 and 93 are positioned in form members 94 and 95, each of which is provided with twenty-four apertures through which the lower ends of the contact fingers 92 and 93 project. The assembled sets of contact fingers are positioned in the corresponding rectangular apertures 90 and 9I, as indicated in Figure of the drawings, and wedge members 95 and 91 in the form of short lengths of copper wire are driven between the free ends in order to secure them in frictional contact engagement with the sides of the rectangular apertures 90 and 9 I. The entire assembly is then dipped in molten solder in order to provide a substantially unitary construction.

The upper ends of the contact fingers 92 and 93 are bowed outwardly, and silver inserts 98 and 99, in the form of silver rivets, are positioned therein on the outer sides thereof for contact engagement with corresponding narrow strips of silver I00 and MI that are rolled into thin copper strips I02 and I 03 which are sweated into suitable recesses in the inner surfaces of the switch blades I9 and 80, as illustrated.

Housings I09 and I01, formed preferably of cast hard bronze, are suitably secured to the base members 88 and 89, and they are provided with suitably flanged portions that extend over and between the sets of contact fingers 92 and 93 for the purpose of guarding them and preventing unintended distortion thereof. It will be noted that the bolt 8| on which the switch blades 19 and 80 are rotatably mounted extends through the housing I01. It will further be observed that the silver inserts 98 and 99, in the upper bowed out portions of the contact fingers 92 and 93, project slightly through the open sides of the housings I06 and I01, for example as illustrated in Figure 11. In this position the inserts 98 are positioned slightly within the path of relative movement with the silver strips I00 in the switch blades 19 and 80 so that on movement thereof from the position illustrated in Figure 11 to the switch closed position as shown in Figure 10, the upper ends are moved inwardly slightly to provide the desired contact engagement. The contact pressure between the engaging silver surfaces is provided not alone by the limb of the contact finger 92, for example, in which the silver insert 98 is positioned, but in addition, the other limb serves to back up the first limb in providing contact pressure, as will be readily understood.

It will now be apparent that substantially point contact engagement takes place between each of the contact fingers 92 and 93 and the corresponding silver strips or inserts I00 and IOI in the inner faces of the switch blades I9 and 80. Since the contact engaging portions are solid silver, the contact resistance of which remains low and substantially constant, the desired contact condi tions will always be present. This will be true even if the switch blade 18 remains in the open or closed position for a considerable period.

As shown more clearly in Figure 13 of the drawings, the silver strip I00 is relatively narrow and thin. This small amount of silver is required since a plurality of aligned point contact engagements are had therewith as distinguished from surface contact engagement. It is possible to place the silver strip I on the copper insert I02 which, itself, is' d by a soldering operation into the blade 80. this manner tlisilver strip I00 is in y bonded to the switch blade 80.

As indica in Figures 14 and 15, the open ends of the contact finger 02 are rounded, while the upper ends are flattened along the inner surface thereof. This construction facilitates the drilling of the apertures for the silver inserts or rivets 98 and, at the same time, increases the flexibility of the fingers.

As indicated hereinbefore, the operating mechanism 82 is provided to move the switch blade 18 and to lock and unlock it. The construction of this mechanism is illustrated more clearly in Figure 9 of the drawings where it will be observed that this mechanism comprises an operating member H2, the left hand end of which is bifurcated and rotatably mounted on the transverse bolt 83, while the right hand end is provided with a pull ring H3 that is adapted to be engaged by a hook stick. The operating member H2 is formed preferably of cast hard bronze, and it is provided with downwardly extending spaced apart projections H4 which are arranged to engage the rivet 84 for the purpose of limiting the rotation of the operating member H2 about the bolt 83. Rotatably mounted on the bolt 83 and between the bifurcated end portions of the operating member H2 is a latch I I5 that is biased in a counterclockwise direction by a spring H5, one end of which engages the latch H5 and the other end engages the rivet 84, the main portion of the spring being disposed around the bolt 83, as illustrated. The latch H5 is arranged to engage a hook II! that is cast integrally with the housing I06 for holding the switch blade I8 in the closed position. The inward movement of the switch blade 18 is limited by the engagement of the rivet 84 with a pair of lugs H8 that are cast integrally with the housing I 06. Suitable interfitting projections are provided on the operating member H2 and on the latch H5 to cause rotation of the latter out of engagement with the hook I I! when the pull ring H3 is rotated in a clockwise direction. By the time that the right hand projection I I4 has engaged the transverse rivet 84, the latch H5 will have been moved out of engagement with the hook H1. The continued application of force to the pull ring H3 then causes the switch blade I4 to move together therewith as a unit to the open position.

When the switch is to be closed, the pull ring H3 is operated in the opposite direction. A limited rotation thereof takes place relative to the switch blade I8 until the left hand projection H4 engages the transverse rivet 84. It then moves as a unit with the switch blade 18 to the switch closed position. Sufficient lost motion is provided between the operating member H2 and the latch H5 to permit it to ride up the inclined surface of the hook H! against the biasing force of the spring H6 for engagement with the hook portion thereof when the switch blade 18 is operated to the switch closed position.

It is important that the silver band 25 be mounted on the copper ring 21 rather than being directly mounted on the contact member 23, Figure 2, for the purpose of providing the desired contact surface characteristics. In like manner it is important that the silver strip I00 be mounted in the copper strip I02 rather than being mounted directly in the switch blade 80,

Figure 15. In the former case the silver band 25 and the copper ring 21 will initially be parts of a relatively long cylinder formed of these materials with the silver being rolled into the copper or being secured thereto m? ion welding process. The desired length is cut' rom the cyI inder formed by these two metals to provide the arrangement shown in Figure 2. Likewise the silver strip I00 is rglled into or secured by fusion welding to the copper strip I02. In the initial form a relatively long strip is provided and it is cut up into suitable lengths as desired for insertion in the switch blades 19 and 80.

If an attempt were made to solder the thin strip of silver to the copper switch blade or switch member it would be necessary to use a high conductivity silver solder and to heat the switch blade or switch Ffiembe? to a relatively high temperature in order to eifect the necessary fusion. This heating would anneal the switch blade and destroy its mechanical stiffness. If on the other hand a low temperature lead-tin solder is employed to attach the silver strip to the switch blade or switch member, the lead and tin in the soft solder will alloy with the thin silver strip, which is of the order of 8 or thousandths of an inch thick, with the result that, instead of having a contact surface of pure silver, the contact surface would comprise an uncertain alloy of lead, tin and silver, since under the heat necessary to effect the fusion, the lead and tin will penetrate entirely through the thin silver strip. When the silver strip is backed up with the copper strip, the first difficulty of the an-,,

healed copper blade or switch member is avoided as well as the second difficulty of contaminating the silver contact surface with the lead and tin of the solder. The copper backing strip may then be soldered with soft solder onto the switch blade or switch member and, since it is of appreciable thickness, it is not possible for the soft solder to penetrate through the copper and into the silver strip. It will be obvious that this method of handling the silver strip makes practical the use of this expensive material in commercial shop assembly practice by placing the thin silver strips in such form that they may be handled by the ordinary mechanic. It is then possible to machine the switch blades without reference to the silver and then to add the silver strip backed with copper as one of the final steps in the assembly.

In order to insert the silver bearing copper strip the switch blades are placed in a milling machine and slots are milled therein as indicated in Figure 12. After the slots are cleaned out they are swabbed with a soldering flux, preferably of the acid type, and then the silver bearing copper strips are clamped in place with an aluminum plate preferably being positioned on the face thereof. The switch blade is then heated to the flow temperature of lead-tin solder which is fed into the ends of the slots. The assembled blade is then permitted to cool in an to the setting temperature of the solder. Tl'e blade is then quenched in water and the clamp is removed. The surplus flux is removed by washing the blade in hot water and then the surplus solder is removed from the face of the blade and it is smoothed with an emery cloth and polished with a wire brush. These steps constitute the final work that is done on the switch blades before they are assembled into the switch proper.

Care must be taken in assembling the silver inserts or rivets 50 in the contact fingers 44, Figure 2, and the silver inserts or rivets 98 in L U U,

MAKERS d BREAKERS,

the contact fingers 92, Figure 15. The hole for receiving the silver insert is first drilled and then countersunk from both sides. This is done after the contact fingers have been formed. The fingers are then dipped in a cleansing solution to remove any impurities that may remain in the drilled holes. The holes are then silver plated in a cyanide or other solution after which they are washed and rinsed in hot water and then the rivets or inserts are inserted and the heads formed in a riveting machine.

It is desirable to plate the copper surface inside of the drilled hole in the contact fingers in order to protect it from oxidation between the time that it is dipped in the cleansing solution and the time when the rivets are inserted. A further reason for plating the holes lies in the tendency for a coating of copper oxide to develop between the silver insert and the copper contact finger because of slight imperfections of fit. As a practical matter it is not possible to provide a smooth surface inside of the drilled holes and when this surface is plated with a silver, the roughness is sufiiciently covered to prevent any contact with air, especially that entrapped between the silver rivet and the copper wire surfaces. Oxidation of the copper surface has a tendency to increase the electrical resistance of the silver rivet contact but by this method the chances of oxidation are practically constant.

In view of the foregoing it will be apparent that special precautions must be taken in the application of silver or silver alloy in the construction of switches to form the contact engaging portions therebetween. It is important that these precautions be taken for the further reason that silver or silver alloy is an expensive material and it is desirable to use a minimum weight of it in each switch in order to reduce the cost thereof to a competitive figure.

Since certain further changes may be made in the above constructions and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A switch comprising, in combination, a pair of switch members mounted for relative movement to open and close an electric circuit, one of said switch members comprising a pair of spaced apart contact members, the other of said switch members being arranged and adapted to engage both of said contact members, insert means in said contact members and said other of said switch members of a material other than that of which they are composed forming the contact engaging portions therebetween, the insert means in said contact members being secured therein by wedging action and the insert means in said other switch member comprising a narrow strip embedded in a wider strip of material of substantially the same character as that of which said other switch member is composed, spring means biasing said contact members in opposite directions into the path of relative movement of said switch members, stop means for limiting the movement of said contact members to positions slightly inside of said path whereby said spring means is prestressed before said other switch member engages said contact members, and additional stop means for limiting the relative movement of said switch members towardthe Lxdll'linef circuit closed position such that said insert means in said contact members are substantially centered on said narrow insert strip whereby the width required of the same is reduced.

2. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a plurality of pairs of oppositely spaced apart contact fingers each secured at one end to one of said switch members and having a silver insert secured near the other end by wedging shoulder means, insert means integrally bonded to said other switch member and disposed to be engaged by said silver inserts, said insert means comprising a narrow strip of silver adapted to be engaged by said silver inserts and embedded in a wider strip of material of substantially the same character as that of which said other switch member is composed, said silver inserts being so shaped as to provide a substantially point contact engagement with said silver strip means, resilient means biasing each contact finger of each pair in opposite directions to provide a predetermined contact pressure between said silver inserts and said silver strip means, and additional stop means limiting the relative movement of said switch members toward the circuit closed position for centering the silver inserts in contact engagement with said silver strip means thereby reduc ing the width required of the same.

3. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a pair of contact members on one switch member each having a contact surface defining a volume and one of said contact members enclosing the other, and a pair of sets of contact fingers on the other switch member each set being individual to one of said contact members and aligned therewith, each finger of each set being arranged and adapted to have limited contact engagement with the contact surface individual thereto.

4. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a pair of contact members on one switch member each having a contact surface defining a volume and one of said contact members enclosing the other, a pair of sets of contact fingers on the other switch member each set being individual to one of said contact members and aligned therewith, each finger of each set being arranged and adapted to have limited contact engagement with the contact surface individual thereto, and strips of silver on said contact surfaces and silver inserts in said contact fingers forming the contact engaging portions therebetween.

5. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a plura ity of contact members on one switch member each having a cylindrical contact surface and said contact surfaces being concentric. and a plurality of rows of contact fingers on the other switch member each row being individual to one of said contact members and aligned with the contact surface thereof, each finger of each row being arranged and adapted to have substantially point contact engagement with the contact surface individual thereto.

6. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a plurality of contact members on one switch member each having a cylindrical contact surface and said contact surfaces being concentric, a plurality of rows of contact fingers on the other switch member each row being individual to one of said contact members and aligned with the contact surface thereof, each finger of each row being arranged and adapted to have substantially point contact engagement with the contact surface individual thereto, and a band of silver integrally bonded to each of said contact surfaces and a silver insert in each of said contact fingers forming the contact engaging portions therebetween.

7. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a plurality of contact members on one switch member each having a cylindrical contact surface and said' contact surfaces being concentric. a plurality of rows of contact fingers on the other switch member each row being individual to one of said contact members and aligned with the contact surface thereof, each finger of each row being arranged and adapted to have substantially point contact engagement with the contact surface individual thereto, resilient means individual to each of said rows of contact fingers for biasing them into contact engagement with said contact surfaces, and means for limiting the movement of said contact fingers to positions slightly within the path of relative movement with said contact surfaces.

8. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a plurality of contact members on one switch member each having a cylindrical contact surface and said contact surfaces being concentric, a plurality of rows of contact fingers on the other switch member each row being individual to one of said contact members and aligned with the contact surface thereof, each finger of each row being arranged and adapted to have substantially point contact engagement with the contact surface individual thereto, a band of silver integrally bonded to each of said contact surfaces and a silver insert in each of said contact fingers forming the contact engaging portions therebetween, resilient means individual to each of said rows of contact fingers for biasing them into contact engagement with said contact surfaces, and means for limiting the movement of said contact fingers to positions slightly within the path of relative movement with said contact surfaces.

9. A device for opening and closing an electric circuit comprising, in combination,- a pair of relatively movable switch members, a pair of contact members on one switch member each having an outwardly facing cylindrical contact surface and said contact surfaces being concentrio, and a pair of concentric rows of wires fastened at one end on the other switch member, each of said rows of wires being individual to one of said contact members for engagement with the contact surface thereof, said wires having portions adjacent their outer ends bent to provide limited contact engagement of each wire with the cooperating contact surface.

10. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a pair of contact members on one switch member each having an outwardly facing cylindrical contact surface and said contact surfaces being concentric, a pair of concentric rows of wires fastened at one end on the other switch member, each of said rows of wires being individual to one of said contact members for engagement with the contact surface thereof, said wires having portions adjacent their outer ends bent to provide limited contact engagement of each wire with the cooperating contact surface, and a narrow band of silver on each of said contact members and a silver insert in each of said wires at the bent portion thereof forming the contact engaging portions therebetween.

11. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a pair of contact members on one switch member each having an outwardly facing cylindrical contact surface and said contact surfaces being concentric, a pair of concentric rows of wires fastened at one end on the other switch member, each of said rows of wires being individual to one of said contact members for engagement with the contact surface thereof, said wires having portions adjacent their outer ends bent to provide limited contact engagement of each wire with the cooperating contact surface, a coil tension spring embracing each of said rows of wires at said bent outer end portions for biasing said wires inwardly into contact engagement with said contact surfaces, and means individual to each of said wires for individually limiting the inward movement thereof to positions slightly within the path of relative movement with said contact surfaces.

12. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, a pair of contact members on one switch member each having an outwardly facing cylindrical contact surface and said contact surfaces being concentric, a pair of concentric rows of wires fastened at one end on the other switch member, each of said rows of wires being individual to one of said contact members for engagement with the con tact surface thereof, said wires having portions adjacent their outer ends bent to provide limited contact engagement of each wire with the cooperating contact surface, a narrow band of silver on each of said contact members and a silver insert in each of said wires at the bent portion thereof forming the contact engaging portions therebetween, a coil tension spring embracing each of said rows of wires at said bent outer end portions for biasing said wires inwardly into contact engagement with said contact surfaces, and means individual to each of said wires for individually limiting the inward movement thereof to positions slightly within the path of relative movement with said contact surfaces.

13. A switch contact member comprising, in combination, a base member, a pair of rows of contact fingers secured to said base member and defining a pair of concentric open cylinders, a spring embracing each row of fingers and urging them inwardly of said cylinders, and means limiting the extent of the inward movement of each of said rows of contact fingers.

14. A switch contact member comprising, in combination, a base member, a row of contact fingers secured to said base member and defining an open cylinder, a spring embracing said row of fingers and urging them inwardly, and stop means carried by said base member and individual to each of said wires for individually limiting the extent of the inward movement thereof.

15. A switch contact member comprising, in combination, a base member, a pair of concentric rows of wire contact fingers secured at one end to said base member, each of said fingers having a portion adjacent itsouter end bent to provide a contact surface of limited area facing inwardly, a silver insert in said bent portion forming the contact surface and conforming to the shape of said finger, a coil tension spring embracing each of said rows of contact fingers at said bent outer end portions for biasing said fingers inwardly, and stop means carried by said base member and individual to each of said fingers for individually limiting the extent of the inward movement thereof.

16. A switch contact member comprising, in combination, a base member, a pair of concentric rows of wire contact fingers secured at one end to said base member, each of said fingers having a portion adjacent its outer end bent to provide a contact surface of limited area facing inwardly, a silver insert in said bent portion forming the contact surface and conforming to the shape of said finger, a coil tension spring embracing each of said rows of contact fingers at said bent outer end portions for biasing said fingers inwardly, and a cylindrical stop member individual to each of said rows of wire contact fingers, each stop member being mounted at one end on said base member and having an inturned flange at the other end substantially in alignment with the outer ends of the contact fingers individual thereto, each flange having a radially slotted aperture individual to each finger for limiting the radial movement and preventing twisting thereof.

17. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members. one of said switch members having a cylindrical contact surface, a plurality of spring wire contact fingers carried by the other switch member and disposed in such manner as to define an open cylinder for contact engagement with said contact surface, and a cylindrical stop member secured at one end on said other switch member and having a flange at the other end substantially in alignment with the outer ends of said contact fingers, said flange having a radially slotted aperture individual to each finger for limiting the radial movement thereof to a position slightly within the path of relative movement with said contact surface and for preventing twisting thereof on engagement therewith.

18. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, one of said switch members having an outwardly facing cylindrical contact surface. a plurality of wire contact fingers carried by the other switch member and disposed in such relation as to define an open cylinder, each of said fingers having a portion adjacent its outer end bent to provide a contact surface of limited area facing inwardly. spring means embracing said contact fingers at the bent outer portions thereof for biasing them inwardly, a cylindrical stop member secured at one end on said other switch member and surrounding said contact fingers, and a flange extending inwardly from the other end of said stop member having radially slotted apertures therein in which the outer ends of said fingers are individually positioned, said apertures being of such length as to permit said contact surfaces of limited area to be positioned slightly within the path of relative movement with said cylindrical contact surface and of such width as to prevent distortion of said fingers on operation to the circuit closed position.

19. A device for opening and closing an electric circuit comprising. in combination, a pair of relatively movable switch members, one of said switch members having an outwardly facing cylindrical contact surface, a plurality of wire contact fingers carried by the other switch member and disposed in such relation as to define an open cylinder, each of said fingers having a portion adjacent its outer end bent to provide a contact surface of limited area facing inwardly, a narrow band of silver on said cylindrical contact surface and a silver insert in each of said contact fingers at the bent portion thereof forming the contact engaging portions therebetween, spring means embracing said contact fingers at the bent outer portions thereof for biasing them inwardly, a cylindrical stop member secured at one end on said other switch member and surrounding said contact fingers, and a flange extending inwardly from the outer end of said stop member having radially slotted apertures therein in which the outer ends of said fingers are individually positioned, said apertures being of such length as to permit said contact surfaces of limited area to be positioned slightly within the path of relative movement with said cylindrical contact surface and of such width as to prevent distortion of said fingers on operation to the circuit closed position.

20. In combination, a pair of U-shaped wire contact members having the ends of the limbs thereof rigidly connected, a cooperating contact member having two spaced apart contact surfaces facing each other and each individual to one of said wire contact members. means for effecting individual contact engagement between each contact surface and the wire contact member individual thereto, and a silver insert in each of said contact members adjacent the junction of said limbs facing outwardly and a silver strip in each of said contact surfaces forming the contact engaging portions therebetween.

21. A switch comprising, in combination; a pair of contact assemblies positioned in insulated spaced relation, each of said assemblies comprising a pair of parallel rows of upstanding inverted U-shaped contact fingers rigidly secured at the lower ends and having the upper ends bowed outwardly to form contact surfaces of limited area; a pair of spaced apart switch blades having contact surfaces facing each other and each arranged and adapted to be moved into and out of contact engagement with a row of said contact fingers of each of said contact assemblies, and a silver insert in each of said contact fingers and silver strips integrally bonded in the contact surfaces of said switch blades forming the contact engaging portions therebetween.

22. A switch comprising, in combination; a pair of stationary contact members. each of said contact members comprising a flat base, a pair 0. parallel rows of hairpin shaped contact finger: rigidly secured at the open ends in said base and having the upper ends bowed outwardly, and a housing secured to said base and extending over said rows of contact fingers and having open sides through which said bowed ends project; a pair of mechanically interconnected switch blades rotatably mounted on opposite sides of one of said housings and having contact surfaces facing each other for simultaneously engaging the bowed ends of said fingers of both said contact members, and a silver insert in the outermost portion of each of said contact fingers and a narrow strip of silver in said contact surfaces of said switch blades individual to each row of con tact fingers of each contact member forming the contact engaging portions therebetween.

23. A switch member comprising, in combination, a plate-like base member, a pair of parallel rectangular apertures extending longitudinally thereof, a plurality of hairpin shaped contact 10 fingers having the open ends positioned in each of said apertures, wedge means between said free ends holding said contact fingers in position, the portions adjacent the outer ends of said contact fingers being provided with double convex surfaces to permit substantially point contact engagement therewith, and a silver insert in said double convex surface of each of said contact fingers and conforming to the shape thereof to provide the contact engaging portion.

24. A device for opening and closing an electric circuit comprising, in combination, a pair of relatively movable switch members, one of said switch members having a contact surface, a plurality of contact fingers carried by the other switch member for contact engagement with said contact surface, spring means common to all said contact fingers for biasing them into engagement with said contact surface in the circuit closed position, and guide and stop means carried by said other switch member and co-operating with said contact fingers for guiding and limiting the individual movement thereof to position them slightly within the path of relative movement with said one switch member.

ALLAN RAMSEY. 

